The treatment of the skin with topical compositions has been known is since the dawn of civilization. Today, a wide variety of skin treatment compositions are available to the consumer including moisturizers, anti-acne compositions, sunscreens, make-ups, topical anesthetics, artificial tanning compositions, skin lightening compositions, anti-wrinkle compositions, and the like.
As the number of skin treatment products grows, so does the need for providing products which deliver improved benefits to consumers. For example, it is desirable to provide products which are easy to apply and which form a smooth, uniform film upon the skin surface. It is desirable to provide products which are not greasy or sticky and which have an aesthetically appealing skin feel. It is desirable to provide products which can be used to deliver active ingredients to the skin and which are substantive such that the active ingredient is not easily lost from the skin by rub-off, wash-off, perspiration, or overly-rapid penetration through the skin.
Examples of topical products that are particularly difficult to formulate are those containing an active ingredient that is potentially irritating to the skin, and those that utilize a costly active ingredient. In the case of products in which the active ingredient is potentially irritating to the skin, it is desirable to obtain the benefit from the active while minimizing the potential skin irritation effects. In the case of products in which the active is costly, it is desirable to maximize the benefit from the active while minimizing the amount of active to be formulated. For example, with sunscreen products, it is a challenge for formulators to maximize the sun protection from the sunscreen active or actives while minimizing the potentially irritating effects of the active and also keeping down formulation costs by utilizing the lowest level of sunscreen possible.
It is, therefore, seen from the above discussion that topical skin care compositions can be improved in a variety of ways.
One approach to improving topical skin care products is by the addition of film-forming polymers and thickeners. However, most film-forming polymers and thickeners tend to be greasy and sticky, thereby imparting undesirable aesthetic qualities to the product. Many of these materials also have less than ideal rheological properties and yield products that are stringy, lumpy, and difficult to apply to the skin. Many of these materials can only be used over a narrow formulation pH range. Also, many of these materials are incompatible with various active ingredients.
It is found in the present invention that highly useful oil-in-water emulsion compositions can be prepared by utilizing the particulate thickener materials described herein to thicken the oil phase of the emulsion. These particulate thickeners overcome many of the disadvantages of conventional film-forming polymers and thickeners. These particulate thickeners are known for use in industrial products such as coatings, adhesives, and sealants, but have seen relatively little use in the personal care products area.
The emulsions of the present invention also utilize at least one oil phase emulsifier or at least one aqueous phase emulsifier.
The oil phase of these emulsions is thickened to achieve a relatively high viscosity, i.e., from about 3000 cps, measured at 25.degree. C. using a Brookfied RVT viscometer equipped with a T bar "B" spindle rotating at 5 rpm, to about 10,000,000 cps, measured at 25.degree. C. using a Brookfied RVT viscometer equipped with a T bar "F" spindle rotating at 0.5 rpm, which, surprisingly, yields emulsions with highly desirable characteristics. It is found that these emulsions are nongreasy and nonsticky and have a smooth feel. These emulsions are easy to apply and spread upon the skin and form a smooth, uniform film upon the skin surface. These emulsions can be formulated over a wide pH range and are compatible with a large variety of active ingredients. These emulsions are also useful for delivering sunscreen actives and other actives which are potentially irritating to the skin.
It is, therefore, an object of the present invention to provide oil-in-water emulsion compositions that are useful for topical application to human skin.
It is another object to provide emulsions which are not sticky or greasy and which are aesthetically pleasing to the user.
It is another object of the present invention to provide emulsions which can be formulated over a wide range of pH values and which are compatible with a wide range of active ingredients.
It is another object of the present invention to provide emulsions which are highly substantive and which also provide substantivity for any active ingredients.
It is another object of the present invention to provide emulsions which are nonirritating to human skin and which help to mitigate the effects of potentially irritating active ingredients.
It is another object of the present invention to provide emulsions in which mitigate the penetration of potentially irritating actives through the skin.
It is another object of the present invention to provide emulsions which also comprise at least one sunscreen active and which are useful for providing protection against the harmful effects of ultraviolet radiation.
It is another object of the present invention to provide methods of treatment of human skin with the oil-in-water emulsions described herein.
These and other objects will become readily apparent from the detailed description which follows.